On Thu, Feb 5, 2009 at 12:55 PM, Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote: > On Wed, 4 Feb 2009 15:27:45 -0800 (PST) > Davide Libenzi <davidel@xxxxxxxxxxxxxxx> wrote: > >> On Wed, 4 Feb 2009, Andrew Morton wrote: >> >> > On Wed, 4 Feb 2009 15:18:43 -0800 (PST) >> > Davide Libenzi <davidel@xxxxxxxxxxxxxxx> wrote: >> > >> > > > > Simple test here: >> > > > > >> > > > > http://www.xmailserver.org/eventfd-sem.c >> > > > > >> > > > > >> > > > > Signed-off-by: Davide Libenzi <davidel@xxxxxxxxxxxxxxx> >> > > > > >> > > > > +/* >> > > > > + * CAREFUL: Check include/asm-generic/fcntl.h when defining >> > > > > + * new flags, since they might collide with O_* ones. We want >> > > > > + * to re-use O_* flags that couldn't possibly have a meaning >> > > > > + * from eventfd, in order to leave a free define-space for >> > > > > + * shared O_* flags. >> > > > > + */ >> > > > > +#define EFD_SEMAPHORE (1 << 0) >> > > > > #define EFD_CLOEXEC O_CLOEXEC >> > > > > #define EFD_NONBLOCK O_NONBLOCK >> > > > > >> > > > > +#define EFD_SHARED_FCNTL_FLAGS (O_CLOEXEC | O_NONBLOCK) >> > > > > +#define EFD_FLAGS_SET (EFD_SHARED_FCNTL_FLAGS | EFD_SEMAPHORE) >> > > > >> > > > How would you recommend that userspace determine whether its kernel >> > > > supports this feature, bearing in mind that someone might backport this >> > > > patch into arbitrarily earlier kernel versions? >> > > > >> > > > What should be userspace's fallback strategy if that support is not >> > > > present? >> > > >> > > #ifdef EFD_SEMAPHORE, maybe? >> > >> > That's compile-time. People who ship binaries will probably want >> > to find a runtime thing for back-compatibility. >> >> I dunno. How do they actually do when we add new flags, like the O_ ones? >> > > Dunno. Probably try the syscall and see if it returned -EINVAL. Does > that work in this case? As youll have seen by now, Ulrich and I noted that it works. > If so, it would be sensible to mention this in > the description somewhere as the approved probing method and to > maintain it. I'll add something to the man page, as this patch progresses. Cheers, Michael -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ git://git.kernel.org/pub/scm/docs/man-pages/man-pages.git man-pages online: http://www.kernel.org/doc/man-pages/online_pages.html Found a bug? http://www.kernel.org/doc/man-pages/reporting_bugs.html -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
